This invention relates to a HST system driven tractor which interposes therein a HST type speed changer to steplessly change the driving speed forwardly and backwardly, in which a driving power transmission route and a PTO (power take off) power transmission route are branched from a pump shaft and a motor shaft at the HST type speed changer, so that both the driving power transmission routes are effectively arranged in double steps in a transmission casing.
The conventional driving power transmisison structure providing the HST type speed changer in a small tractor is well known as disclosed in the U.S. Pat. Nos. 4,304,141 and 4,513,834.
Such prior art also branches the PTO system power transmission route and drive system power transmission route from the pump shaft and motor shaft at the HST type speed changer, but since the PTO system and drive system are arranged longitudinally of the tractor body, the transmission casing becomes longitudinally longer and a mid PTO shaft is disposed in front thereof to place a lawn mower frontward of the tractor body, resulting in that there is an inconvenience that a wheelbase between the front and rear wheels is larger.